diff --git a/sys/dev/cxgb/cxgb_main.c b/sys/dev/cxgb/cxgb_main.c
index 82008e843e6..fb420044901 100644
--- a/sys/dev/cxgb/cxgb_main.c
+++ b/sys/dev/cxgb/cxgb_main.c
@@ -982,7 +982,7 @@ cxgb_makedev(struct port_info *pi)
 #define CXGB_CAP (IFCAP_VLAN_HWTAGGING | IFCAP_VLAN_MTU | IFCAP_HWCSUM | \
     IFCAP_VLAN_HWCSUM | IFCAP_TSO | IFCAP_JUMBO_MTU | IFCAP_LRO | \
     IFCAP_VLAN_HWTSO | IFCAP_LINKSTATE)
-#define CXGB_CAP_ENABLE (CXGB_CAP & ~IFCAP_TSO6)
+#define CXGB_CAP_ENABLE CXGB_CAP
 
 static int
 cxgb_port_attach(device_t dev)
@@ -2059,8 +2059,8 @@ cxgb_ioctl(struct ifnet *ifp, unsigned long command, caddr_t data)
 		}
 		if (mask & IFCAP_RXCSUM)
 			ifp->if_capenable ^= IFCAP_RXCSUM;
-		if (mask & IFCAP_TSO4) {
-			ifp->if_capenable ^= IFCAP_TSO4;
+		if (mask & IFCAP_TSO) {
+			ifp->if_capenable ^= IFCAP_TSO;
 
 			if (IFCAP_TSO & ifp->if_capenable) {
 				if (IFCAP_TXCSUM & ifp->if_capenable)
diff --git a/sys/dev/cxgb/cxgb_sge.c b/sys/dev/cxgb/cxgb_sge.c
index 207f4fbbbf3..a34dab28b5d 100644
--- a/sys/dev/cxgb/cxgb_sge.c
+++ b/sys/dev/cxgb/cxgb_sge.c
@@ -62,6 +62,7 @@ __FBSDID("$FreeBSD$");
 #include <netinet/in_systm.h>
 #include <netinet/in.h>
 #include <netinet/ip.h>
+#include <netinet/ip6.h>
 #include <netinet/tcp.h>
 
 #include <dev/pci/pcireg.h>
@@ -1492,10 +1493,10 @@ t3_encap(struct sge_qset *qs, struct mbuf **m)
 		check_ring_tx_db(sc, txq, 0);
 		return (0);		
 	} else if (tso_info) {
-		int eth_type;
+		uint16_t eth_type;
 		struct cpl_tx_pkt_lso *hdr = (struct cpl_tx_pkt_lso *)txd;
 		struct ether_header *eh;
-		struct ip *ip;
+		void *l3hdr;
 		struct tcphdr *tcp;
 
 		txd->flit[2] = 0;
@@ -1521,18 +1522,37 @@ t3_encap(struct sge_qset *qs, struct mbuf **m)
 		}
 
 		eh = mtod(m0, struct ether_header *);
-		if (eh->ether_type == htons(ETHERTYPE_VLAN)) {
-			eth_type = CPL_ETH_II_VLAN;
-			ip = (struct ip *)((struct ether_vlan_header *)eh + 1);
-		} else {
-			eth_type = CPL_ETH_II;
-			ip = (struct ip *)(eh + 1);
-		}
-		tcp = (struct tcphdr *)(ip + 1);
+		eth_type = eh->ether_type;
+		if (eth_type == htons(ETHERTYPE_VLAN)) {
+			struct ether_vlan_header *evh = (void *)eh;
 
-		tso_info |= V_LSO_ETH_TYPE(eth_type) |
-			    V_LSO_IPHDR_WORDS(ip->ip_hl) |
-			    V_LSO_TCPHDR_WORDS(tcp->th_off);
+			tso_info |= V_LSO_ETH_TYPE(CPL_ETH_II_VLAN);
+			l3hdr = evh + 1;
+			eth_type = evh->evl_proto;
+		} else {
+			tso_info |= V_LSO_ETH_TYPE(CPL_ETH_II);
+			l3hdr = eh + 1;
+		}
+
+		if (eth_type == htons(ETHERTYPE_IP)) {
+			struct ip *ip = l3hdr;
+
+			tso_info |= V_LSO_IPHDR_WORDS(ip->ip_hl);
+			tcp = (struct tcphdr *)(ip + 1);
+		} else if (eth_type == htons(ETHERTYPE_IPV6)) {
+			struct ip6_hdr *ip6 = l3hdr;
+
+			KASSERT(ip6->ip6_nxt == IPPROTO_TCP,
+			    ("%s: CSUM_TSO with ip6_nxt %d",
+			    __func__, ip6->ip6_nxt));
+
+			tso_info |= F_LSO_IPV6;
+			tso_info |= V_LSO_IPHDR_WORDS(sizeof(*ip6) >> 2);
+			tcp = (struct tcphdr *)(ip6 + 1);
+		} else
+			panic("%s: CSUM_TSO but neither ip nor ip6", __func__);
+
+		tso_info |= V_LSO_TCPHDR_WORDS(tcp->th_off);
 		hdr->lso_info = htonl(tso_info);
 
 		if (__predict_false(mlen <= PIO_LEN)) {